title: Suicide seasonality: complex demodulation as a novel approach in epidemiologic analysis.
abstract: BACKGROUND
  Seasonality of suicides is well-known and nearly ubiquitous, but recent evidence showed inconsistent patterns of decreasing or increasing seasonality in different countries. Furthermore, strength of seasonality was hypothesized to be associated with suicide prevalence. This study aimed at pointing out methodological difficulties in examining changes in suicide seasonality. METHODODOLOGY/PRINCIPAL FINDINGS: The present study examines the hypothesis of decreasing seasonality with a superior method that allows continuous modeling of seasonality. Suicides in Austria (1970-2008, N = 67,741) were analyzed with complex demodulation, a local (point-in-time specific) version of harmonic analysis. This avoids the need to arbitrarily split the time series, as is common practice in the field of suicide seasonality research, and facilitates incorporating the association with suicide prevalence. Regression models were used to assess time trends and association of amplitude and absolute suicide numbers. Results showed that strength of seasonality was associated with absolute suicide numbers, and that strength of seasonality was stable during the study period when this association was taken into account.
  
  
  CONCLUSIONS
  Continuous modeling of suicide seasonality with complex demodulation avoids spurious findings that can result when time series are segmented and analyzed piecewise or when the association with suicide prevalence is disregarded.
authors.affiliation: Department of Basic Psychological Research, School of Psychology, University of Vienna, Vienna, Austria. ingo.nader@univie.ac.at
authors.forename: Ingo W
authors.initials: IW
authors.lastname: Nader
authors.forename: Jakob
authors.initials: J
authors.lastname: Pietschnig
authors.forename: Thomas
authors.initials: T
authors.lastname: Niederkrotenthaler
authors.forename: Nestor D
authors.initials: ND
authors.lastname: Kapusta
authors.forename: Gernot
authors.initials: G
authors.lastname: Sonneck
authors.forename: Martin
authors.initials: M
authors.lastname: Voracek
mesh_terms: D001317:Austria / Q000453:epidemiology; D002423:Cause of Death; D015340:Epidemiologic Research Design; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D012621:Seasons; D012931:Social Environment; D013405:Suicide / Q000706:statistics & numerical data* / Q000639:trends